The present invention relates generally to providing network services such as load balancing, packet filtering or Network Address Translation (NAT). Network services are provided using service managers that send instructions to forwarding agents that are integrated into a routing infrastructure. Those instructions are managed by the forwarding agents and service managers. Instructions are sent from service managers to forwarding agents on a need to know basis to minimize the management burden.
As the IP protocol has continued to be in widespread use, a plethora of network service appliances have evolved for the purpose of providing certain network services not included in the protocol and therefore not provided by standard IP routers. Such services include NAT, statistics gathering, load balancing, proxying, intrusion detection, and numerous other security services. In general, such service appliances must be inserted in a network at a physical location where the appliance will intercept all flows of interest for the purpose of making its service available.
FIG. 1 is a block diagram illustrating a prior art system for providing a network service. A group of clients 101, 102, and 103 are connected by a network 110 to a group of servers 121, 122, 123, and 124. A network service appliance 130 is physically located in the path between the clients and the servers. Network service appliance 130 provides a service by filtering packets, sending packets to specific destinations, or, in some cases, modifying the contents of packets. An example of such modification would be modifying the packet header by changing the source or destination IP address and the source or destination port number.
Network service appliance 130 provides a network service such as load balancing, caching, or security services. In providing security services, network service appliance 130 may function as a proxy, a firewall, or an intrusion detection device. For purposes of this specification, a network service appliance that acts as a load balancer will be described in detail. It should be noted that the architecture and methods described are equally applicable to a network service appliance that is functioning as one of the other above described devices.
Network service appliance 130 is physically located between the group of servers and the clients that they serve. There are several disadvantages to this arrangement. First, it is difficult to add additional network service appliances when the first network service appliance becomes overloaded because the physical connections of the network must be rerouted. Likewise, it is difficult to replace the network service appliance with a back up network service appliance when it fails. Since all packets pass through the network service appliance on the way to the servers, the failure of the network service appliance may prevent any packets from reaching the servers and any packets from being sent by the servers. Such a single point of failure is undesirable. Furthermore, as networks and internetworks have become increasingly complex, multiple services may be required for a single network and inserting a large number of network service appliances into a network in places where they can intercept all relevant packet flows may be impractical.
The servers may also be referred to as hosts and the group of servers may also be referred to as a cluster of hosts. If the group of servers has a common IP address, that IP address may be referred to as a virtual IP address (VIPA) or a cluster address. Also, it should be noted that the terms client and server are used herein in a general sense to refer to devices that generally request information or services (clients) and devices that generally provide services or information (servers). In each example given it should be noted that the roles of client and server may be reversed if desired for a particular application.
A system that addresses the scalability issues that are faced by network service appliances (load balancers, firewalls, etc.) is needed. It would be useful to distribute functions that are traditionally performed by a single network element and so that as much function as possible can be performed by multiple network elements. A method of coordinating work between the distributed functions with a minimum of overhead is needed.
Although network service appliances have facilitated the development of scalable server architectures, the problem of scaling network service appliances themselves and distributing their functionality across multiple platforms has been largely ignored. Network service appliances traditionally have been implemented on a single platform that must be physically located at a specific point in the network for its service to be provided.
For example, clustering of servers has been practiced in this manner. Clustering has achieved scalability for servers. Traditional multiprocessor systems have relatively low scalability limits due to contention for shared memory and I/O. Clustered machines, on the other hand, can scale farther in that the workload for any particular user is bound to a particular machine and far less sharing is needed. Clustering has also facilitated non-disruptive growth. When workloads grow beyond the capacity of a single machine, the traditional approach is to replace it with a larger machine or, if possible, add additional processors within the machine. In either case, this requires downtime for the entire machine. With clustering, machines can be added to the cluster without disrupting work that is executing on the other machines. When the new machine comes online, new work can start to migrate to that machine, thus reducing the load on the pre-existing machines.
Clustering has also provided load balancing among servers. Spreading users across multiple independent systems can result in wasted capacity on some systems while others are overloaded. By employing load balancing within a cluster of systems the users are spread to available systems based on the load on each system. Clustering also has been used to enable systems to be continuously available. Individual application instances or machines can fail (or be taken down for maintenance) without shutting down service to end-users. Users on the failed system reconnect and should not be aware that they are using an alternate image. Users on the other systems are completely unaffected except for the additional load caused by services provided to some portion of the users that were formerly on the failed system.
In order to take full advantage of these features, the network access must likewise be scalable and highly available. Network service appliances (load-balancing appliances being one such example) must be able to function without introducing their own scaling limitations that would restrict the throughput of the cluster. A new method of providing network services using a distributed architecture is needed to achieve this.
In a large network, a service manager may control a large number of flows routed through a large number of forwarding agents. In many such networks, the packets for any given flow tend to follow the same path, and therefore always arrive at the same routers. In such a complex network, it may be impractical for a service manager to register instructions or filters for how to deal with each individual flow with every router. In addition, it may be impractical for each router to store all of the instructions relating to flows that do not ever pass through the router.
What is needed is a system whereby service managers only register filters or instructions for specific flows at routers in the path of the flow. This would reduce the overhead on each router for maintaining filters and on the service manager for synchronizing filters.
A system is disclosed that includes a service manager that determines how a network service is provided for a flow and sends instructions to routers that detect packets for the flow when such packets are actually detected by the routers. Instructions for flows that follow a consistent path are only stored in routers that are in the path. For flows that do not always follow a consistent path, instructions for the flow are determined by the service manager the first time a packet in the flow is detected by a router. When another packet is detected at a new router, then the original instructions are found by the service manager and forwarded to the new router. This arrangement also allows service managers to continue to provide network services without interruption and without reconfiguration when network topology is changed. New routers in the path of a flow request instructions from the service manager and the service manager sends the existing instructions to the new router. Instructions stored in routers no longer in the flow may eventually be timed out.
It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication lines. Several inventive embodiments of the present invention are described below.
In one embodiment, a method of providing instructions for forwarding packets includes broadcasting a general instruction specifying a plurality of flows to a plurality of forwarding agents and receiving at a service manager a first message responsive to the general instruction indicating that a packet for a specific flow has been received by a specific forwarding agent. A specific instruction is generated at the service manager for handling the specific flow and the specific instruction for handling the specific flow is sent to the specific forwarding agent.
In another embodiment, a method of providing instructions for forwarding packets includes broadcasting a general instruction specifying a plurality of flows to a plurality of forwarding agents and receiving at a service manager a first message from a first forwarding agent responsive to the general instruction indicating that a packet for a specific flow has been received by the first forwarding agent. Specific instructions are generated at the service manager for handling the specific flow and the specific instructions for handling the specific flow are sent to the first forwarding agent. The service manager receives a second message from a second forwarding agent responsive to the general instruction indicating that a packet for a specific flow has been received by the second forwarding agent; and sends the specific instructions for handling the specific flow to the second forwarding agent.
In another embodiment, a service manager includes a forwarding agent sending interface configured to broadcast a general instruction specifying a plurality of flows to a plurality of forwarding agents and a forwarding agent receiving interface configured to receive messages from the forwarding agents responsive to the general instruction indicating that a packet for a specific flow has been received by one of the forwarding agents. A processor is configured to generate a specific instruction at the service manager for handling the specific flow and the forwarding agent sending interface is further configured to send the specific instruction for handling the specific flow to the one of the forwarding agents.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures which illustrate by way of example the principles of the invention.